Poly(metaphenylene isophthalamides) are useful in a wide variety of commercial applications. The outstanding performance characteristics of these polymers under stress and at high temperatures have made them useful in the form of bushings, seals, electrical insulators, compressor vanes and impellers, pistons and piston rings, gears, thread guides, cams, brake linings, and clutch faces. These polymers are often prepared in the form of coalescible powders. The powders can be formed into the desired final shape by molding techniques or can be formed into stock shapes, such as rods, tubes and sheets which can be machined into the desired final form.
The unusual thermal characteristics of poly(metaphenylene isophthalamides) have required special molding techniques. Although these compositions are linear polyamides, their melt viscosity is so high that they cannot be considered to be thermoplastic as the term is normally understood. In the past, as noted in Jordan, U.S. Pat. No. 3,413,394, shaped articles were made by coalescing powders of these and similiar materials using elevated pressures of from 3,000 to 30,000 psi while simultaneously heating in excess of 300.degree. C. However, these high temperatures and pressures had to be maintained for a considerable period of time, severely limiting production capability. Accordingly, as described in the Jordan patent and Turnbull, U.S. Pat. No. 3,925,323, coalescing techniques were developed which first pressed the coalescible powder into the desired final configuration under high pressures of from 10,000 to 100,000 psi and then separately heating the resulting preform to a temperaure of 250.degree. C. or higher. While this two-stage coalescing technique provided desirable products, it still required the use of special apparatus to exert the high pressures required in the first stage of the operation, and often failed to provide satisfactory shaped articles having a maximum dimension greater than about 3 inches.